PubMed Health⌕ Search

Biomedical subjects

B V Sastry

Publications and source records attributed to B V Sastry.

At least 91 records · Page 5Linked to original sources
PubMed1976

The influence of mecamylamine on contractions induced by different agonists and on the role of calcium ions in the isolated rabbit aorta.

The exposure of helically cut strips of rabbit aorta to mecamylamine (1 mM) for 5 minutes blocked the histamine (3.25 muM)-induced contractions completely and reduced those induced by potassium (25mM, 68%) without affecting contractions induced by norepinephrine (3.0 muM, NE) or acetylcholine (10 muM). Mecamylamine, by itself, did not exhibit agonist activity, but it increased the contractile tension of the muscle which was contracted by NE. The responses to NE were either enhanced or not affected by small doses of mecamylamine (1 mM), but were partially blocked by large doses of mecamylamine (10 mM). The antagonism exhibited by mecamylamine in low doses (1 mM) against the above agonists was reversible. The shape of the response to NE on the muscle, which was treated with a high dose of mecamylamine (20 mM) and washed, was significantly different from that of the control. Our results are consistent with the following conclusions: 1) Mecamylamine in low doses (1 mM) blocks the histamine receptor and therefore the histamine-induced contractions. Two molecules of mecamylamine are competitive with 1 molecule of histamine. 2) Mecamylamine blocks the potassium-induced contractions, but does not block completely the calcium influx in the potassium-depolarized muscles. Therefore, it may interfere partially with the utilization of extracellular or loosely bound calcium during potassium-induced contractions. 3) Mecamylamine in high doses (10 mM) partially blocks norepinephrine-induced contractions by affecting firmly bound calcium stores. 4) Procaine antagonizes the effects of NE, histamine and acetylcholine by affecting, at least partially, the firmly bound calcium stores.

Acetylcholine↗
PubMed1976

Effects of calcium antagonist, 6-(N, N-diethylamino) hexyl-3, 4, 5-trimethoxybenzoate, on digitalis-induced arrhythmias and cardiac contractions.

6-(N, N-Diethylamino) hexyl-3, 4, 5-trimethylbenzoate (TMB-6) and lidocaine were equipotent (1 mg/kg) in the conversion of ectopic rhythms to normal rhythms in digoxin-toxic dogs. However, TMB-6 had fewer side effects on heart rates and dp/dt than lidocaine. TMB-6 inhibited the contractile force of electrically stimulated dog and guinea-pig atria and ventricles at concentrations ranging from 2.5 X 10(-5) to 1.7 X 10(-4) M. Elevation of extracellular Ca++ concentrations from 2.7 to 5.4 mM produced a significant increase in the ID50 of TMB-6 in atria (from 2.5 X 10(-5) to 5.0 X 10(-5) M in dogs and from 7.2 X 10(-5) to 1.0 X 10(-4) M in guinea pigs). TMB-6 (7.3 X 10(-5) to 2.4 X 10(-4) M) depressed the amplitude of Ca++-dependent action potentials in depolarized dog cardiac Purkinje fibers. These results are discussed with regard to the antagonism of TMB-6 on Ca++ availability in the myocardium which leads to the conversion of cardiac arrhythmias.

Action Potentials↗
PubMed1976

Anticholinergic activities of D(-)R- and L(+)S-mandeloylcholines.

The nature of the antagonism of the D(-)R- and L(+)S-mandeloylcholines to acetylcholine (ACh) was investigated at the muscarinic receptors of the guinea-pig ileal longitudinal muscle. The nature of the inhibition of acetylcholinesterase (AChE) and serum cholinesterase (ChE) by the mandeloylcholines was also investigated. Both optical isomers of mandeloylcholine were reversible competitive antagonists of ACh at the muscarinic receptors. One molecule of mandeloylcholine combined with one receptor. The apparent affinities (1/KB, where KB = dissociation constant) of the mandeloylcholines were in the following order: homatropine greater than D(-)R-mandeloylcholine greater than DL(+/-)RS-mandeloylcholines = L(+)S-mandeloylcholine. Therefore, the mandeloylcholines were stereoselective for muscarinic receptors. The mandeloylcholines were (mixed) reversible inhibitors (competitive and noncompetitive) of ACh hydrolysis by AChE. There was no significant difference between the apparent K1 values of the mandeloylcholines in the inhibition of AChE. The mandeloylcholines were mixed reversible inhibitors (competitive and noncompetitive) of ChE. D(-)R-mandeloylcholine had a higher apparent K1 than its isomer.

Animals↗
PubMedDate not supplied

Maternal tobacco smoking and changes in amino acid uptake by human placental villi: induction of uptake systems, gammaglutamyltranspeptidase and membrane fluidity.

Maternal smoking depressed the active uptake of amino acids by human placentae and lowered their levels in the placenta and umbilical vein. During starvation of cells for amino acids, more amino acid carriers are induced and incorporated into the plasma membrane. A question arises whether there could be similar changes due to maternal smoking in the placental amino acid uptake carrier systems. Therefore, the characteristics of (a) the uptake of 2-amino[I-14C]-isobutyric acid (AIB) by isolated placental villi, (b) gammaglutamyltranspeptidase (GGTP), a critical enzyme of the gammaglutamyl cycle (GGC) for the uptake of amino acids in human placenta, and (c) lipid structural parameters (reciprocal of fluidity), by steady state fluorescence polarization of plasma membrane vesicles of microvilli (MV) and microsomal membranes (MM) of umbilical and chorionic plate arteries of placentae of smoking and non-smoking mothers were investigated. The above investigations gave the following results: (a) Washed placental villi of smokers exhibited higher capacity for AIB uptake than those of non-smokers. The higher uptake capacity was mainly due to increase in Vmax for AIB uptake in smokers. Km increased for placental AIB uptake in smokers. (b) Maternal smoking lowered GGTP activity of MV by decreasing its Vmax. Therefore, maternal smoking decreases the formation of gammaglutamyl-amino acid (GGAA) on the surface of trophoblast which are absorbed by the trophoblast. The degree of absorption of GGAA is considered as an inverse environmental signal for the cell to regulate amino acid transport systems. Maternal smoking seems to decrease the formation and absorption of GGAA and thereby induce the formation of new carriers for AIB uptake. (c) Maternal smoking increased the values for lipid structural order parameters and microviscosity of MV and induced tolerance against fluidization by ethyl alcohol in MM of umbilical and chorionic arteries. The alterations could increase Km for AIB uptake system and decrease the sensitivity of umbilical and chorionic arteries to vasoconstrictive substances like 5-hydroxytryptamine and catecholamine which are released by nicotine. All these changes tend to overcome the deficits produced in placental amino acid transport and satisfy the demands of the growing fetus for amino acids.

Amino Acids↗
PubMedDate not supplied

Subtype of muscarinic receptor coupled to the attenuation of hormone-stimulated cAMP accumulation in NG108-15 neuroblastoma x glioma hybrid cells.

The subtype of muscarinic receptor which mediates cAMP attenuation is not established. Therefore, several selective muscarinic antagonists were used to characterize the subtype of muscarinic receptor coupled to the inhibition of hormone-stimulated cAMP accumulation using NG108-15 neuroblastoma x glioma hybrid cells. These cells were prelabeled with [2-3H]-adenine, washed, and resuspended in a culture medium containing the phosphodiesterase inhibitor 3-isobutyl-1-methylxanthine (0.5 mM). The labeled cells were preincubated with the different antagonists 12-15 min. before they were challenged with agonists. The formation of [3H]-cAMP was activated by PGE1 (1 microM) or forskolin (1 microM). In all cases, [3H]-cAMP formed was separated and measured. Carbachol (100 microM) and McN-A343 (10 mM) were used as standard muscarinic agonists. These studies gave the following results: a) McN-A343 (10 mM), an M1 receptor agonist, was only a partial agonist causing 40% inhibition of cAMP accumulation indicating that this effect was not mediated by an M1 receptor; b) The M1-selective antagonist, pirenzepine, exhibited low affinity (pA2 6.2) further suggesting that an M1 receptor was not coupled to the attenuation of cAMP accumulation; c) Two selective M2 antagonists (AF-DX 116 and methoctramine) and M3 antagonist (HHSiD) were used to further characterize these muscarinic receptors. The order of all antagonists based on their affinities (pA2 values) could be arranged in the following order: atropine (9.0) > methoctramine (7.6) > HHSiD (6.9) > AF-DX 116 (6.6) > pirenzepine (6.2). HHSiD exhibits the same degree of affinity to M2 receptors of other tissues as it does to those of NG cells.(ABSTRACT TRUNCATED AT 250 WORDS)

1-Methyl-3-isobutylxanthine↗